M60 Swap tachometer reading

[Garageaholic]

Its a square wave

[OoPEZoO]

So its just a square wave that changes frequency with RPM? I'm assuming its at a 5 volt logic level? And you guys need to cut the frequency exactly in half?

Just trying to make sure I know exactly what you need.

[JGood]

Cut in half if using a 4 cyl plug... cut by 1.5x if using a 6 cyl plug (which is what I'm going to use, unless I can find a 4 cyl plug easily). This is second hand knowledge, I didn't really dive into this at all yet.

[OoPEZoO]

Dividing by 2 (for a 4cyl plug) is super simple due to just being able to use a basic flip flop, but dividing by 1.5 will take a more complicated circuit and possibly some trial and error. I would be really interested to know the frequency range used by the tach circuit. If I knew that, I could simulate it on my bench and test some things out.

[JGood]

Dividing by 2 (for a 4cyl plug) is super simple due to just being able to use a basic flip flop, but dividing by 1.5 will take a more complicated circuit and possibly some trial and error. I would be really interested to know the frequency range used by the tach circuit. If I knew that, I could simulate it on my bench and test some things out.

Yeah, that's all a bit over my head. It's been years since I've messed with circuits, and there's been one too many beers between then and now, lol.

If you want to mess with it, I've got a few extra gauge clusters and stuff laying around. But I'm not sure any of that would help without having the input from the DME to measure the actual signal.

[garretvs]

Have you checked if the M60 system outputs at a 4-cylinder frequency? Many V8's put out pulses at 4x, just like a 4-cylinder. Maybe all you need is a 4-cylinder coding plug on the back of the cluster.

[Jonsku]

Have you checked if the M60 system outputs at a 4-cylinder frequency? Many V8's put out pulses at 4x, just like a 4-cylinder. Maybe all you need is a 4-cylinder coding plug on the back of the cluster.

Noup, that doesn't work. You need to half the signal.

Try searching with the keywords I gave earlier, they've discussed it quite a lot online..



The code-plugs shouldn't be too hard to come by. You can buy the whole instrument cluster for $20 or something anyways..

[OoPEZoO]

Yeah, that's all a bit over my head. It's been years since I've messed with circuits, and there's been one too many beers between then and now, lol.

If you want to mess with it, I've got a few extra gauge clusters and stuff laying around. But I'm not sure any of that would help without having the input from the DME to measure the actual signal.

I could walk you through it all. Its not rocket science, more like electronics 101. That being said.......ideally, it would be great to see waveforms or know the frequency range versus RPM for the E30 4cyl, 6cyl, and the V8 you are using. With that information, it would be a breeze to come up with a solution. Without that info, it is a real guessing game that will involve trial and error. I'll do some more searching and see what I can come up with.

Where do you end up putting the circuit? I mean, does it go between the ignition coil and DME, between the DME and the cluster, between the cluster and coding plug, between the coding plug and tach??? I'm assuming it goes between the DME and the cluster, but I've never had the need to research it.

[g3n0cid3]

Here is the cheapest way using a single flip flop circuit.

http://www.electronics-tutorials.ws/counter/count_1.html

If it is a square wave this will work.

[Jonsku]

Where do you end up putting the circuit? I mean, does it go between the ignition coil and DME, between the DME and the cluster, between the cluster and coding plug, between the coding plug and tach??? I'm assuming it goes between the DME and the cluster, but I've never had the need to research it.

This is how I understand it;

-RPM-signal goes from DME to coding plug (square wave)
-The frequency of the signal depends on number of cylinders you have (# of pulses per second for example)
-6cyl has 3 or 6 pulses
-4cyl has 2 or 4 pulses
-8cyl has 4 or 8 pulses

The "form" of pulses is the same, thus all you need to do is to cut out part of them.

[robiniscool]

just in case anyone is wondering dakota digital sgi-8 works great :up:
just plug, wire and play ($94 shipped from summit)...... well at least for my car

[mark///m3]

just in case anyone is wondering dakota digital sgi-8 works great :up:
just plug, wire and play ($94 shipped from summit)...... well at least for my car

So with this and the 4 cylinder coding plug?

[robiniscool]

So with this and the 4 cylinder coding plug?

actually it doesnt matter what plug you have, theres two settings you dial up in it, one is how many cylinder your engine has and the other is how many cylinder your tach reads, it does 4, 6, 8, 10 cyl. pretty cool electronic....
but i do have a 4 cyl coding

http://www.dakotadigital.com/pdf/sgi-8d.pdf

in case your wondering on how to use

[JGood]

Yeah, I've had my Dakota Digital converter installed for about 4 months and 2k miles now, works great. It's easy to use, well packaged, and fairly cheap.

[mark///m3]

actually it doesnt matter what plug you have, theres two settings you dial up in it, one is how many cylinder your engine has and the other is how many cylinder your tach reads, it does 4, 6, 8, 10 cyl. pretty cool electronic....
but i do have a 4 cyl coding

http://www.dakotadigital.com/pdf/sgi-8d.pdf

in case your wondering on how to use

Awesome thanks, I was going to order my plug up but I'll give this a try with my six cylinder plug and report back.